Langmuir Adsorption Isotherm
Adsorption is a separation process that is widely used in the manufacturing sector as well as in our daily lives. Adsorption processes take advantage of some materials’ capacity to concentrate specific chemicals from liquids onto their surfaces. Thus, interacting fluids with such particles may achieve the desired goal of purification or separation. Once equilibrium is established between the adsorbent and its contacting solution, the extent of adsorption in a given circumstance is determined. In practice, the mass transfer of the species between the solution and the adsorbent surfaces, as well as the adsorption reaction rate, have a substantial influence on adsorption performance.
The desired concentration of species on the surfaces of adsorbing materials, which drives adsorption, governs two additional processes: chromatography and ion exchange. Adsorption, ion exchange and chromatography are sometimes grouped under the umbrella phrase “sorption processes.”
Chromatography, like most adsorption techniques, operates in a fixed-bed mode but is designed to separate liquid mixtures through an intermittent feed of the solution, followed by the passage of an elution solution. The charged groups in the solid substance used in ion exchange interact with the charged ions in the liquid solution.
In 1918, Langmuir proposed the first coherent theory of adsorption onto a flat surface based on kinetics; that is, there is a continuous process of bombardment of molecules onto the surface and corresponding evaporation of molecules from the surface to maintain zero rates of accumulation at the surface at equilibrium.
The Langmuir model makes the following assumptions:
- The surface is homogenous, which means that the adsorption energy is constant across all spots.
- Adsorption on the surface is localised, which means that adsorbed molecules or atoms are adsorbed at specific, localised spots.
- Each site can only hold one molecule or atom.
The Langmuir theory is founded on a kinetic principle: The adsorption meaning and the rate of adsorption, which is the striking rate at the surface multiplied by a sticking coefficient, also known as the accommodation coefficient, equals the rate of desorption from the surface.
Basic Concept of Adsorption
Adsorbate – It refers to the guest molecules that concentrate at the active surface of the adsorbent; from an adsorption standpoint, these substances, whether gaseous or liquid, are the targets that should be removed from the bulk of the system and gathered onto the adsorbent.
Adsorbent – The term adsorbent or sorbent refers to a highly porous, large specific surface area of solid or liquid with uniform/diverse particle size lattice vacancies, homogeneous/heterogeneous pore structures, and These solid materials are available in various shapes, such as rods, mouldings, spheres, discs, or monoliths, with particle sizes ranging from nano to micro to macroscales.
With the increasing availability of different types of adsorbents nowadays, and the more recent interests in biotechnology and green technology, there has been a significant expansion in the applications of adsorption in many areas.